linux-kernel - Re: [PATCH] SLUB: revert direct page allocator pass through

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Message-Id: <200901240212.58829.nickpiggin@yahoo.com.au>
Date:	Sat, 24 Jan 2009 02:12:57 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Pekka J Enberg <penberg@...helsinki.fi>,
	yanmin_zhang@...ux.intel.com, Andi Kleen <andi@...stfloor.org>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] SLUB: revert direct page allocator pass through

On Saturday 24 January 2009 02:03:22 Christoph Lameter wrote:
> On Fri, 23 Jan 2009, Nick Piggin wrote:
> > Hmm, it lists quite a number of advantages that I guess are being
> > reverted too? What was the test case(s) that prompted this commit
> > in the first place? Better ensure it doesn't slow down...
>
> The advantage was mainly memory savings and abilty to redefined kmallocs
> to go directly to the page allocator. Totally avoids slab allocator
> overhead.

Well it sounds in the changelog like a massive performance advantage.
Unfortunately it doesn't really say what the workload was.


> I thought higher order allocations were not supposed to be used in
> performance critical paths?

? You use them all the time in SLUB alone.


> Didnt you want to do everything with order-0
> allocs?

People don't always do what I think is best, unfortunately ;)


> It seems that we currently need the slab allocators to compensate for the
> performance problems in the page allocator for these higher order allocs.
> I'd rather have the page allocator fixed but things are as they are.

No objections from me with speeding up the page allocator of course.


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